/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.function.server;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.charset.StandardCharsets;
import java.util.function.Function;

import reactor.core.publisher.Mono;

import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.server.PathContainer;
import org.springframework.util.Assert;
import org.springframework.util.ResourceUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.util.pattern.PathPattern;
import org.springframework.web.util.pattern.PathPatternParser;

/**
 * Lookup function used by {@link RouterFunctions#resources(String, Resource)}.
 *
 * @author Arjen Poutsma
 * @since 5.0
 */
class PathResourceLookupFunction implements Function<ServerRequest, Mono<Resource>> {

    private static final PathPatternParser PATTERN_PARSER = new PathPatternParser();

    private final PathPattern pattern;

    private final Resource location;


    public PathResourceLookupFunction(String pattern, Resource location) {
        Assert.hasLength(pattern, "'pattern' must not be empty");
        Assert.notNull(location, "'location' must not be null");
        this.pattern = PATTERN_PARSER.parse(pattern);
        this.location = location;
    }


    @Override
    public Mono<Resource> apply(ServerRequest request) {
        PathContainer pathContainer = request.pathContainer();
        if (!this.pattern.matches(pathContainer)) {
            return Mono.empty();
        }

        pathContainer = this.pattern.extractPathWithinPattern(pathContainer);
        String path = processPath(pathContainer.value());
        if (path.contains("%")) {
            path = StringUtils.uriDecode(path, StandardCharsets.UTF_8);
        }
        if (!StringUtils.hasLength(path) || isInvalidPath(path)) {
            return Mono.empty();
        }

        try {
            Resource resource = this.location.createRelative(path);
            if (resource.exists() && resource.isReadable() && isResourceUnderLocation(resource)) {
                return Mono.just(resource);
            }
            else {
                return Mono.empty();
            }
        }
        catch (IOException ex) {
            throw new UncheckedIOException(ex);
        }
    }

    private String processPath(String path) {
        boolean slash = false;
        for (int i = 0; i < path.length(); i++) {
            if (path.charAt(i) == '/') {
                slash = true;
            }
            else if (path.charAt(i) > ' ' && path.charAt(i) != 127) {
                if (i == 0 || (i == 1 && slash)) {
                    return path;
                }
                path = slash ? "/" + path.substring(i) : path.substring(i);
                return path;
            }
        }
        return (slash ? "/" : "");
    }

    private boolean isInvalidPath(String path) {
        if (path.contains("WEB-INF") || path.contains("META-INF")) {
            return true;
        }
        if (path.contains(":/")) {
            String relativePath = (path.charAt(0) == '/' ? path.substring(1) : path);
            if (ResourceUtils.isUrl(relativePath) || relativePath.startsWith("url:")) {
                return true;
            }
        }
        if (path.contains("..") && StringUtils.cleanPath(path).contains("../")) {
            return true;
        }
        return false;
    }

    private boolean isResourceUnderLocation(Resource resource) throws IOException {
        if (resource.getClass() != this.location.getClass()) {
            return false;
        }

        String resourcePath;
        String locationPath;

        if (resource instanceof UrlResource) {
            resourcePath = resource.getURL().toExternalForm();
            locationPath = StringUtils.cleanPath(this.location.getURL().toString());
        }
        else if (resource instanceof ClassPathResource) {
            resourcePath = ((ClassPathResource) resource).getPath();
            locationPath = StringUtils.cleanPath(((ClassPathResource) this.location).getPath());
        }
        else {
            resourcePath = resource.getURL().getPath();
            locationPath = StringUtils.cleanPath(this.location.getURL().getPath());
        }

        if (locationPath.equals(resourcePath)) {
            return true;
        }
        locationPath = (locationPath.endsWith("/") || locationPath.isEmpty() ? locationPath : locationPath + "/");
        if (!resourcePath.startsWith(locationPath)) {
            return false;
        }
        if (resourcePath.contains("%") && StringUtils.uriDecode(resourcePath, StandardCharsets.UTF_8).contains("../")) {
            return false;
        }
        return true;
    }


    @Override
    public String toString() {
        return this.pattern + " -> " + this.location;
    }

}
